OKIDATA ML590 Service Manual page 243

Yes End of procedure.
No Contact Technical Support.
No
Has the problem been resolved?
Yes End of procedure.
No Replace the RS232C board.
Are + 8 vdc / - 8 vdc present on the main control board?
Yes Replace the RS232C board.
Has the problem been resolved?
Yes End of procedure.
No Contact Technical Support.
No
Has the problem been resolved?
Yes End of procedure.
No Contact Technical Support.
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Replace the power supply unit.
Replace the main control board.